I'm TOTALLY a Bernina fan, absolutely. I have um, several, including a 630, 820, and 1030 (my three favs). But...I highly recommend that you test drive the 8900 and a 7 series machine before buying. I would only buy a 7 series if I were able to exhaustively test drive the actual machine I would be getting AND if the dealer agreed to promptly repair the machine in case of any troubles and replace the machine or refund my money in case of the 3rd major issue.
I recommend you read the discussions on Pattern Review. Some new owner of the 7 series have had serious issues. Most dealers have promptly repaired and/or replaced defective machines, some have been resistant. I have total confidence in Bernina to "make it right", but then, I live within driving distance of Bernina USA in Aurora, IL

I think they will work out the bugs, as they did with the 8 series (my 820, made in 2011, has been fabulous and trouble-free). I really wish they would get it right before releasing new models, as it's not fun reading about the trials and tribulations of fellow sewists.
The 8900 has several upgrades/solutions to minor issues on the 7700. The 7700 also had issues when it came out, and a friend of mine had hers replaced when she finally contacted Janome USA after her dealer left her hanging. She's now thrilled with her 830. I think both brands are very good quality. If I didn't already have plenty of machines, not to mention an abiding love for Bernina presser feet, the foot controller, and my Bernina dealer, I would definitely test drive an 8900 and a Pfaff Creative Performance (which is available with or without emboirdery, with two module sizes) before buying a 7 or 8 Series Bernina.
Just my opinion...