I bought some 3M Wet n Dry paper from a seller on ebay and the difference is like night and day. The finish after the using the 3M, 600 grit and then 1200, is just a duller finish, still as smooth and flat as the original panel but just without the deep colour and shine. No scratches or gouges, it's obviously been sanded but it's a smooth as the proverbial baby's bottom. The other paper bought from a well known on line screw retailer left a lot of small scratches. Don't get me wrong, it still did the job but will require an awful lot more work to bring the finish back to a reasonable level.
The 3M paper is more expensive, quite a bit more actually but considering the time, money and effort going into this project it's a small price to pay. One downside is that because it's essentially a trade product it's a little hard to find and when you do, it's not available in small quantities coming in either packs of 25 for the courser grains or 50 for the finer. I found a seller on ebay willing to split some packs for me so I got a few different grades for the price of one. Having said all that and having seen the difference I wouldn't hesitate in springing for a full pack next time around. The 3M website gives a list of suppliers if you get stuck. www.3m.com