A bit of a gauge issue

I have one finished item to show off. A cardigan for my [future] Godson, made with two balls of Sirdar Donegal Tweed. The pattern is Baby Vertebrae by Kelly Brooker - I really love her patterns, they are clearly written and fun to knit. It's intended for his birthday in July.

This is my latest victim knitwear model wearing the Beyond Puerperium (another Kelly Brooker pattern) I made for his baby shower.

The reason why I'm knitting things in March for a July birthday? He has a twin... Hopefully she'll like one in this yarn:

I've finished the body on my Harvest Moon cardigan. I love the i-cord cast off (OK, I didn't love the time it took, but I love the look it gives) on the body. Now I'm onto the sleeves. To get gauge I knitted the body on 4mm needles, but the sleeves are on DPNs and I seem to be knitting tighter on those, which isn't something I've particularly noticed before, although I've read it can happen. This is what the first sleeve looks like on 4mm DPNs, and there is a noticeable difference and it felt tighter when I tried it on, so I had to pull that bit out and try on 4.5mm instead. That seems to be a lot better!