Hey Benjy,
I did a similar thing on a record a few years ago where we had 3 options at mastering...
To Mastering, we brought:
1. Straight off the mix bus (in-the-box 24Bit-96kHz)
2. The 1/2 masters (ATR-102)
3. The Record-Repro captured back in via nice A/D's (no print through)
In the end, we ended up going with #1 (straight off the digital mix bus). The Mastering Engineer felt, and we agreed after doing some listening, that the analog (and of course the A/D capture of the 1/2") felt like it was down a generation, and didn't sound as good. If you feel like the mixes are feeling a little harsh, the the 1/2 might just be the ticket, but when you A-B them, the difference in depth and detail is quite apparent.
If you're mixing on a desk, make sure you capture the 2-mix with a really nice A/D, or better yet, take Terry's suggestion and try to score one of those Korg DSD recorders. I still think DSD is the closest thing to the real audio.
Still though, if you're going to print to 1/2", there's no better long-term archival medium really... Well worth buying the tape...
Just some thoughts,
Cheers,
JB