FTTC speeds

[#1]

I've been on PN FTTC about 10 days now. Line profile is~38Mb and stable, so thats good. I've had no dropouts to speak of, and I'm very pleased with the connection (compared to the old 4Mb ADSL link, it's a revelation). Not a major issue, but I'm noticing wildly varying download speeds. I'm using the standard speed checkers, and downstream speed is peaking around ~34Mb, but falling to ~21Mb at other times, and not just at the peak hours of 7-10pm. Upstream speeds are totally consistent at around 1.8Mb with only a few Kb here or there difference.
Is this normal, and should I expect these variances? As I'm on the fibre extra package, I assume there's no throttling going on. As there are no errors reported on the PPoE router, I just need to know that what I'm experiencing is normal for FTTC. I am fully aware that there will always be some differences, but 13Mb variance sounds a lot.

[#2]

Yes, it is normal and down to contention at various places on the BT network at various times. Also speed checkers are not that reliable anyway which can add to the perceived problem.
Also because of the faster speeds, even small periods of contention can effect the speeds much more than a lower speed connection.

[#3]

Great, thanks for the reply. It's good to know that everything is normal then! I guess we're all expecting amazing things from fibre broadband, and while it delivers on most fronts, as more people jump onboard, it's the BT infrastructure that's going to feel the pain.
I know speed checkers aren't always reliable, but I've been using the same one to build up a picture of speeds over the last week, and it's been varying wildly.