Taylormade RAC OS II - How do they compare to modern clubs?

I currently use a set of Taylormade RAC OS II's from 6 - PW (I use TM Burner hydrids for 5 & 3).

They are now around 7 years old and have seen plenty of golf, but it is only the last year that I have taken the game seriously. I recently joined a club and my first handicap is 24.0, I hope to reduce it to <20 this year.

I was fitted for the clubs when I first bought them (+1" and 2° up). I consider them to be too upright for me now; this combined with their age is making me begin to think about changing them.

What I am unsure of is whether to replace them with another set of game improvers or go for something more akin to a players club, such as the Mizuno MP-59.

I appreciate that the only way to buy clubs is by trying them and having them properly fitted. But I don't want a like for like replacement only to find my game has improved beyond them in 12-18 months (I wish!).

Would the advances in club technology make current game improvers so significantly different from my RAC's, that I could gain real short-term benefit and find them suitable all the way to a good mid-handicap? Or, would it be prudent to invest in something like the MP-59 that may impact may game in the short-term but have longer term benefits?