IDK to be honest I dont really think it matters much if the guy is a 4.0 or a 4.5.
I have been playing in a mixed doubles league for several years now and from my experience the matches are almost always decided by which male can break down/exploit the other teams female the most often.
I am a 4.0 and so is my partner but we have played against every variation of the 3.5-4.5 pairings.
It boils down to every male either overpowering, spinning, or exploiting the opposing teams female player.
I rarely (if ever) see a 4.0 male that cannot easily handle a 4.0 woman and most of the time even the 3.5 men can handle 4.0 women because even if the woman has good strokes her movement is always the deal breaker. Women react slower and are less explosive in their movement so its all too easy to get them deep then hit it short and win the point.
Whether the guy is 4.5 or not really isnt a huge difference unless when his female partner is serving your teams return game isnt good enough to get past him. Usually a 3.5 females serve is "tee time" for the other team and its easy to break her.
Racquet: Wilson PS97 String: Prince syn gut @55lbs in mains, ISOSPEED Baseline Control 16 @50lbs in crosses, Wilson 6.1 95s backup same string setup