MRC LONGWY

Hi,

I'm currently riding a five year old Cannondale six13 which I've been gradually upgraded over the years (Record, Cosmic Carbones etc) and I'm now thinking that maybe the frame should be next.
There's nothing inherently wrong with the current frame, but thought I'd pose the question in the last two bike shops I visited... If I spend a reasonably amount (say £1500) on a new frame, would I really notice the difference? Obviously I got a resounding 'yes' from both shops, the implication being that it would be like night and day, but I thought I'd put the question to a slightly more impartial audience...
I don't race (other than the occasional Duathlon) and most of my road riding is 30 - 50 mile solo rides at say 18mph average.. so for an average enthuiast, would the improvement really be that marked??

Please help.

I didn't find the right solution from the Internet.

References
https://www.bikeradar.com/forums/viewtopic.php?t=12630895
Cloud Solution Video

Thanks