845 has so much solvent in it that I wouldn't bother trying to "layer" it. Plus, it's so durable on its own that it's not really necessary.
As both Dr. G and the Collinite folks pointed out about their own products, it appears the solvents are a moot point. Dr. G. says after sufficient time for crosslinking to occur his product won't be adversely affected by 845. The Collinite folks offer that the solvents in 845 aren't self-stripping, leading one to believe actual layering will occur. Maybe I'm just goofy but I tend to think the manufacturers probably know more about the products they make than anyone else.
As for durability, that's the reason people choose Collinite. 845 looks superb on everything I've ever used it on. Still, on white I've been looking for a little something extra.
After being an 845 devotee for as long as I can remember I started looking at sealants over the last year. I was impressed with the slickness and ease of use of both Jetseal 109 and BFWD. The look on white didn't appear to offer anything above 845, IMO, and there's no comparison to longevity and beading over time.
When I used Opti Seal for the first time I was floored... there was a noticeable difference... on white. I suppose it was that sterile Zaino-like, plastic shine that I've seen referred to. It really made the white finish jump out and grab your attention. The beading is pretty incredible right after application as well. The longevity is reported to be sub par compared to any of the Collinite products though. In an effort to have my cake and eat it too I'd like to have the eye-grabbing effects of Opti Seal as well as the longevity of 845. One thing I noticed about the Opti Seal as well as other LSPs I've used... I drove home in a light rain today and the vehicle looked splashed and dirty. After a drive in the rain after a fresh application of 845 it's almost like dirt doesn't stick. It doesn't
look like it needs washed. One of the nice bonuses of 845 that I've heard numerous people remark on.
Much of what we do, especially to our personal vehicles, may be as much personal perception as reality. It's almost an 'if it feels good, do it' type of endeavor at times. Which is probably why a wise man once said "find something you like and use it often".
After the next wash I think I'll do a wipe down with Last Touch and hit it with 845. Maybe multiple coats. If my personal perception is that it's a good thing then it is. ::::shrug::: Different strokes and all that.
TL