I would go epl5 for sure over the epl3. However, I don't think either the epl5 or em5 achieve 1/320 flash sync as someone said. I think only the em1 does that. epl5 & em5 go to 1/250. epl3 is 1/160 which is the same as epl2 (I shoot an epl2).
I have to very much disagree with the comment that a PEN is not that much of an upgrade over an S95.
I own an S95 and it's a terrific camera for the size and portability and versatility. But, my epl2 is much better for image quality. Some of this goes to lens also. If only using the kit lens on the PENs then you're not getting the full power of these cameras. Make no mistake, it's still better than the S95, but if you put the 60mm macro on you'll get great pictures from any of the PEN line. I use the 60mm and 9-18 on an epl2. I was coming from different P&S cameras underwater and the quality is another level or two.
I also owned a Nikon D7000. An EPL2 is not as good as the nikon but, it's pretty close. Biggest difference is focus speed. I now have an em5 and I'd say it is 98% of a D7000.
I have also purchased an epm1 refurbed body for cheap ($119) and with my 17mm pancake on it, it has completely replaced my S95 as my small carry camera. It's a little larger than the S95, but the quality of the pictures is so much better.
So, after all that, I'm saying you'll take a step up with any of the PENs over the S95.
If you want to change ports and lens often, go with the nauticam and the em5.
However, a very versatile and easy setup is similar to what I have.
You could get the epl5 & oly housing. Then get the ZEN dome for the 9-18mm. This dome will accommodate the 9-18, the 60mm and the 14-42. You can now go semi wide (100 degree view) all the way to very tight macro without ever changing a port.
I use this setup on my epl2 housing and really love the versatility of it. I occasionally do miss being able to go with a fisheye lens, but it's not that big a deal to me.
BTW, I like the oly PEN housings. I think they are well made and ergonomically fit my hand well.
I've never used a pricey aluminum housing, so I might not know what I'm missing.
I find changing shutter/aperture easy. It is with push buttons and not wheels, but fairly straight forward to me.
In manual mode, one push of the top button on the jog wheel enables changing shutter/app with the 4 jog wheel positions. So, you just push the top jog button, then the top/bottom jog buttons will increase/decrease shutter speed and the left/right will increase/decrease aperture. I may have some of those details incorrect, but that's generally how it works. I'm assuming its the same for epl3 & 5. I know the epm1 takes more steps than that.
You have to understand how optical ttl is working to understand why these modes don't work.
I have an Inon D2000 so I'll talk from that perspective, but it's the same in entire inon line and I think sea&sea also.
In inon sttl mode, the strobe is basically watching the camera flash and quelching it's flash at the same time. So, the camera has to be in a mode where it's determing flash duration. Otherwise the external strobe has no timing signal to work off of. If you put the camera in manual flash, which is what you're doing when you select 1/64, then your strobe sees a flash that has nothing to with the exposure for that picture. It's seeing whatever you told the camera strobe to do.
So, if you put the camera in manual flash, your strobe becomes manual.
Now, on an Inon, the way to try and work around this is to use the external auto mode. In this mode, the inon strobe is determining flash duration itself with no input from the camera other than when to start. If using EA mode, then put the camera on 1/64 to save power and quicken refresh time. At this point, you're constricted by the recharge of the inon strobe itself and not the camera. But, from experience, I can tell you that EA is not as consistent in getting the exposure correct as using the cameras ttl with the strobe in sttl.
On my epl2, I'm generally in manual with flash set to fill and my D2000 on sttl.
I find the D2000's recycle time is similar to the epl2 being ready to go again.
Of course, you can always go full manual with camera and strobe as you've already figured out.
Obviously, I'm not Phil, but that is an interesting thing you point on the Olympus site. It's obviously a misprint. Notice that it only gives a view of 62 degrees for a multi focal lens. It should obviously be a range. If you look at dpreview of that lens it list it as 62-100 degrees.
On the olympus site look at the 17mm. It is listed at 65 degrees. The 12mm is 84 degrees.