I think Jim's assessment of Roger and Rafa's rackets are wrong. I also think the specs for Rog and Raf in this thread are not quite right.
Rafa is HL but only 2-4 points HL, with static weight under 12 oz and SW in the 350-360 range.
Roger is HL but around 6-8 points HL, with static weight around 364 grams, and SW in the 350-360 range. I have seen several analysis of Roger's racket and never saw a 330 SW. See Greg Raven's analysis and other TW threads.
I agree with Jim that good 3.5+ level and above players can benefit from poly if they use it wisely. My opinion is using poly as a cross is good for most of us if you want more directional control, a touch more spin, and far less string movement. You will need to change strings every 10-20 hours. If you have a really fast swing or a really powerful tweener style racket than using poly mains with a synthetic cross is fine for rec players.
I was last rated 4.0, was rated 4.5 about 2 decades ago and played 5.0 USTA league 30 years ago and won about 30-40% of matches but official ranking never went to 5.0. I like playing with poly strings for the reasons cited above.