8 C is my usual water temperature during the winter. Air is similar to Jeroen with the occasional freezing morning down to -4, or so.
Personally, I find that there is a big difference between a "cheap" wetsuit and an "expensive" one, even from the same brand. This winter I am using an O'Neill Hyperfreak Fire and a Psycho Tech. Both are 4.5/3.5 mm. On warmer and calmer days when both thicker suits are wet I dig out my spring suit - Patagonia Regulator R1 (3/2 mm I think).I can feel the difference between the Psycho and the Hyperfreak Fire, especially on days with wind chillwhenthe Psycho Tech material on the front and back does a much better job.
Having said that, I think protecting your limbs and head is probably more important. I cannot really get on with the Solite split toe thing and the grip wears out too fast, imo. On cold days I am using my 5mm Vans booties, which are warm and comfortable. I also have a pair of 5mm Wetty booties which are far more comfortable and grippy, but I don't think they are as warm as the Vans. On warmer days and shorter sessions I use my 3mm Wetty booties. What's great about the Wetties is that you can easily turn them inside out when taking them off, thus they dry much faster and easier.
Once the air temps go down, I use 5mm mittens. I find that mittens keep my hands much warmer. I assume this is because the fingers are together helping to warming each other up. Yes, the loss of dexterity is a bit of a bummer, but you get used to it. I really enjoyed the Patagonia mittens last season, but they neoprene around the thumbs disintegrated within one season. This year I am trying the top of the range O'Neil 5mm mittens and I hate them. Fit is weird (they have loosened a lot pretty quickly and now store water after paddling) and grip is nearly non existent. Most days I stick to my 3mm Solite gloves. I bought the thicker lobster split Solite gloves a few weeks ago, but they are super tight around the bottom of the palms and hurt my hands more than the cold. They are the same size as the 3mm Solite gloves, so hopefully I can stretch them out.
Finally, don't forget the hood. With a hood you can stay out much longer and feel more comfortable. I am currently using an O'Neill 2mm psycho tech and also a 3mm Prolimit (Dutch brand I think) one when it's properly cold.
As a bigger chap, I do have some bulk and personal insulation, but I am not some polarbear bro. I grew up with around 21 C winter water temps.