Wow, 13 lbs. is great for such a full-featured, rigid 7x17 camera. Given the weight of a stock 8x10 Sinar P, I would have expected it to be more. David Robert's 8x20 Sinar conversion weighs 24 lbs., but it's an 8x20, uses a Sinar P front function carrier and has two rail supports and an additional base plate. I think your combination of P rear function carrier and F2 front standard gives the best combinatiopn of usability, rigidity and light weight.
I expect my Franken ARCA to come in at around 12 - 12 1/2 lbs. in it's "maximum" configuration. I could probably shave over a pound and a half off the weight if I went with a custom fabricated u-frame for the rear standard. I'm using off the shelf 25mm aluminum extrusions because they were cheap, easy to modiy and just bolt togther. They are rigid, but heavier than they need to be. If I end up using the camera as much as I hope to, I may eventually get a lighter weight, but no less sturdy rear u-frame manufacturered. The geared front standard also adds 3/4 pound to the weight. If I want to go light, I can replace it with a non-geared front standard. I can also swap out the rails and extension bracket for shorter versions and sacrifice a little max. extension to save a little more weight for those longer hikes. Still, even in max config mode, ~12 lbs. for a full featured 7x17 camera with geared front movements isn't bad.
I currently have a Gitzo G1570 head that I bought to use with the 7x17, but like you I noticed there was considerable flex in the top platform. The one I have is the older, heavier non-magnesium version that is pupposedly a little sturdier (and certainly weighs more). I'll try it with my Franken ARCA, but if it proves inadaquate, I may be looking for something else.
Yes, I do wear glasses. Thanks for the tip on the clip on magnifier. I'll give it a try.