Hi Trekkie, for what it's worth I purchased a GM1000 last Friday to have as a second detector to the 4500.
I got out on the weekend to try it out on some pretty hot Vic GT ground and I must say I'm pretty impressed with it.
My history is I've used various VLF's in the past in the Vic GT and maybe because of that I've found the GM so easy to use, basically set it on manual 10 with all metal and swing away, I could easily distinguish between hot rocks, hot ground and genuine targets. No gold found but couldn't believe how many tiny bird shot I was pinging at 2" in very hot ground, I've never dug bird shot that small before, it's just a matter of training your years to listen to the difference in response instead of looking at the meter on the screen as I'm sure you would be used to with the 705.
I wanted a second detector for when I needed a break from swinging the 4500 and couldn't justify the SDC even though I liked the one I was watching in action at a recent meet-up (very impressed with it) but I decided to get the GM1000 and I'm so glad I did.
In my honest opinion after spending a few hours on the weekend with it I would have no hesitation to say if you are thinking of buying one while saving for a SDC then do so as I would be confident you would be very happy with it, the 5" coil is super sensitive and punches deep for it's size, wish I bought one sooner.