Newbie needs advice

swiftish
swiftish Posts: 3
edited January 2018 in Road buying advice
Hi folks,
New on here and keen to get involved. Been road cycling for 18months now and ready now for an upgrade on my Giant Defy, tiara groupset. Have my eye on a Colnago A1R 2017, alloy, 105 groupset. Seems a real bargain at £909 from Merlin cycles. Need advice on the sizing. I'm 5'8" and my Giant is a medium, reckon i can get away with a 49" in the Colnago.
Any thoughts?