Welcome in Ali
I'd stick with the 4xv especially as it mint . A mint 4xv is more desirable than a 5jj .
Now you can skip[ this bit if you like as i'm going to waffle
The 4xv & 5jj are essentially the same bike , the main difference is the tank & body work including the front fairing bracket , slimmer clocks and seat , the only difference i can see whith the seat is the fact that it moulds to the tank differently so is a different shape . The engine has some changes to the head & gearbox but are essentially the same although the upper left hand engine mount in the head changed bolt size on the 5jj to match the 4xv and yamaha introduced the AIS system on the 5jj which a lot of people strip off anyway ( do a search on here for AIS if i remember correctly it's "Air Induction System" or something similar " .
I have a 98 4xv although it's fightered , it now has a 5jj engine in it as the 4xv motor blew & i could only get a 5jj at the time . Some people have questioned my findings due to the carbs possibly being worn but i found that the 5jj has a a stronger smoother midrange which means that the "hit" of the 8-9000 rpm powerband is not as harsh on the 5jj , i swapped the carbs with the 4xv carbs and lost the midrange & that intoxicating 8-9000 rpm "hit" was back again . Form me i prefer the midrange and a carb swap is an hours job , quite easy & you can pick up carbs for anything from £80 ( if wait ) to £250 .
From what i can tell unless they have fitted aftermarket bars theres no real difference between the 4xv & 5jj clip-on's and the forks are the size and fit both bikes although i think they messed with the forks through both the 4xv's & 5jj's due to the different markings on the lowers .
So the main difference i think you'd notice between the two is the midrange/powerband & thats if my carb findings are actually correct .
stick with the 4xv
P.S. have you been on here before or the old forum as your forum name rings a bell