[Bigbottomend]

Maybe try the Antelope out with PT10HD as its audio interface - see how you feel about the latency...as far as the 4,1's limitations, you could get a second computer such as a souped up iMac 27" for more modern software/mixing and keep the old workhorse doing what it does best, which is reliably recording music. Honestly, the modern native systems aren't really any better than HD systems for recording (in fact they may be worse), but they do smoke the old systems when it comes to editing, plugin loads, mixing in the box and bouncing to disk.