Despite not yet having completed my 2008 study in further maths I would likely recommend further if you are in any way similar to me.
I was averaging 90-95% on my unit 1+2 methods sacs whilst doing minimal, work however my unit 1+2 general specialist course (essentially covers the same topics as Unit 3+4 Spec just in slightly less depth) was giving me averages around the 60% mark. Essentially I was doing less work in general specialist than methods simply because it was very difficult to understand topics fully if you didn't pay full attention to the entire course and it's always discouraging when you can't complete questions so you just ending going through periods of not doing anything.
I ended up switching specialist for further maths 3+4 and have not regretted it, any further maths class can be turned into a study period for an impending test on a more complex subject and it is near impossible to fall behind; don't do work for three weeks spend about 3 hours at home and you'll be caught up. It feels like I have only had to do 4.25 subjects this year as further really does require so little effort. My average sac mark this year is 99% ranking me top in a cohort of 75+ including some specialist students. I know a few friends who decided to do specialist and are similarly lazy and they believe they will struggle to get 20-25 raw in specialist doing likely more work than I have had to complete for further. In conclusion, if you truly are lazy, as I am and cherished the pre yr. 11 maths classes which usually meant no work still equated to top marks, do further maths. That said I also know others who are doing specialist and are dedicated to the subject and could likely get 50 scaled, so it really does depend on your attitude towards schooling, and despite what you would like to think if you struggle to do lots of study now you will most likely be the same next yr.
All the Best,
Luke
EDIT: and to lacoste, you essentially can't drop any marks in further maths to get 50, you can lose some marks in your sacs but only if you are still ranked top of your cohort. In specialist you are able to to drop quite a decent number of marks and still get a 50 as the scaling compensates for its relative difficulty, and if you drop no marks you get ~55 SS (almost impossible IMO though).