Effects of LAN link speed being lower than WAN bandwidth

[RumorConsumer]

Weird situation. A cable somebody installed between buildings on this property is very old and only capable of 10mbit link because of unitized wire pairs. Its like CAT 5 or something. The WAN internet connection is capable of 25mbit and comes into building A where people use it just fine. Then in building B, which is the one connected via 10mbit wired link, the internet feels choppier and its not just because its lower bandwidth, more like it feels congested in some weird way. The switch in Building B that receives the 10mibt connection is gigabit. Is there something about the differential that could be causing the choppiness? We're gonna rewire the cable today for gigabit but Im wondering if thats a known symptom? 

[antonis_sp]

Usually on bad cabling, ethernet connections fall back to 10mbit half-duplex, which causes a lot of collisions on transmitted traffic.

[GIdenJoe]

I don't think congestion would be the correct word.
Rather unstable wired connections could simply cause intermittent packet loss which makes the experience choppier.

[PhilipDAth]

Perhaps the cable had higher than normal attention.  Perhaps water had got into it.  Perhaps it was experiencing a lot of CRC errors.

[RumorConsumer]

The half duplex and packet loss thoughts feel the most resonant for this experience. And i just found out the cable is cat6. So it must be a crap wiring job. It’s a vacation house I’m staying at in Italy and, as always, i can’t keep my hands to myself. Thanks all.

[RumorConsumer]

They unplugged it (in the other house) and plugged it back in and it lit up at 100mbit (speed of the switch in house A). Funny. That did it. They will come back and replace the switch soon just to update things to 1gbit. Dont forget to unplug and replug!