The 950 is actually the Whites Prizm 5 with the 950 concentric coil from the MXT (stock coil). It is a generation old now, with the Prizm 6T being the next up the line from the Prizm 5, the 6T has how been superceded by the Coinmaster GT, and the Prizm lineup superceded by the Coinmaster and coinmaster Pro. These are all coin/relic/jewellery machines vs the 705, which can do coins/relics/jewellery and gold with the higher frequency coil and prospecting mode. The Prizm 5 only runs around 8khz, does not have ground balancing, VDI numbers, backlit screen, or VCO all metal mode like the 6G, Coinmaster GT and 705. The prizm 5 only has 2 choices regarding whites coils, but a wide range of NEL and Detech coils are availalble for them.
The actual 950 coil itself has exactly the same windings as the new spider coils on the coinmaster series, so it has also been superceded.
The 705 would be the most versatile detector of the lot, although more expensive, if you are after a gold detector, I probably wouldn't consider any of those whites models, better off with the 705, or one of the Whites gold specific detectors like the GM3, V-Sat, MXT E-Series, or the GMT. Probably the best all-rounder from whites would be the MXT or MXT Pro, which run 14khz, and have a prospecting mode.
With regards to performance, it would probably been in a similar ballpark to the x-terra 305/505, but still without VDI numbers, and ground balancing function, and less choice of coils. I've got the GT Coinmaster, but am still yet to give it a good work over to give an informed opinion as yet.
To sum up, the detector you are looking at would be a good backup park/beach detector (mainly dry sand) and regards to pricing, these regularly go for around the $200-300US mark on ebay in the US. But I feel that if you already have a 705, you would probably end up using that more due to its versatility. With regards to resale, you never know what prices detector will go for these days on ebay/gumtree, but I think you may struugle to get your money back on it, or make a profit. Put it this way, I bought a brand new Coinmaster GT for $400 from the US with accessories, so for a 10 rear old detector, the Prizm 5 may not be the most economical buy at $380. Hope that info helps.