I have been looking at getting a Lynskey Ti frame for a while and I'm trying to narrow down what I think would be my ideal frame.

I am looking at the R350 frame, which they have listed on their Ebay store and I was wondering if anyone has any feedback on this frame, i.e. ride quality and characteristics, frame flex, comfort, etc. There is not much info out there on this specific frame.
(They no longer make this frame, their new version is the R370 with a press fit BB and disc brakes, which I do not want. Their geometry is the same, however - https://lynskeyperformance.com/2017-r370-frameset/)

I have spoken with the guys at Lynskey and they have provided their feedback. They said the R350 would be a good option. They also recommended the Helix, but I'm not crazy about the Helix tube look.
Basically I'm a big guy, 47 y/o, 270lbs range (right now), trying to get down to 225lbs over the next year. I currently ride a Ritchey Breakaway road bike and my ideal is to ride 15-30miles, 4-5 times per week. My longest rides will probably be 40-50miles, once or twice a month, with a century maybe 1-2x/year. Mostly flat riding terrain with moderate hills occasionally. No racing or Gran Fondos planned, but I do like to do sprint intervals or occasionally shorter fast riding. My concern is that I want to get a frame that is not too flexy, but still comfortable for the shorter distances that I will be riding. I won't be doing 4-5 hours in the saddle much. Mainly 1 hour rides. Lynskey offers some "sport riding" frames, but I think they will be too flexy for a guy my size. Am I looking at the wrong frame?

Any advice is appreciated!