Until recently I had a carve 144 which I used as my lightwind board but I now use an iSonic instead. I really enjoyed the 144 and found the drake 490 an excellent fin and got me going easilly (I'm 86kg at the moment
). I doubt however, that a bigger fin will help you much with the 7.2. When the 7.2 gets powered up you may find that a 54 is too big.
I found that using a different model fin in a similar size helped early planing but working on my technique had the biggest effect. I found that by having little battles with my peers really improved my sailing in all areas.
I would try and borrow a different fin and see if that helps you before investing.