Possibly moving from my HD3 PCIX to ??

Folks: quite frankly, I'm still thoroughly confused about my options. I actually have had a very well running PCIX HD3 system for many years, with 2 AD16X and 1 DA16X. Recently our non-profit got a 2009 Quad 4,1 system donated, and I thought it would be a good time to upgrade. What I am confused about are whether I should just get new PCIe cards and PT10 (after upgrading to a 6-core), or if I am going to get appreciable performance boost by investing a whole lot of cash in the new HDX or HD Native system. I would really like to not have to buy new converters if possible, so therein lies our quandary. Could someone comment on the boost of productivity or features from their older accel system to the new. Heck, I wouldn't even mind optimizing our older G5 HD3 system if it made sense. We are not running more than 40 tracks at a time, and do have Waves Platinum on the older system, and I've always seen Pro Tools as a tape alternative. Lastly, I would really like to have a system dedicated to software instruments, which I thought the new Mac could do. All help is appreciated.

Possibly moving from my HD3 PCIX to ??