Yes, the wiring *is* that sensitive. To get the noise rejection of differential signalling down twisted pairs, the pairs need to be both paired, and twisted. Even half an inch of untwistedness, Hextraspeshally for the pair which goes across pins 3-6 (widest separation), can cause much worse performance. Your network will still "work", as the link-layer and upwards will detect garbles and cause retransmits; but your performance will be in the Saniflo and margin for errors decreased.
You may well get away with poor wiring practice: the standards are there so that properly-installed stuff will work over the advertised 100m length at advertised speeds, with the advertised number of plugs and sockets along the way (patch panels, etc.) But as you're d-i-y'ing, do yourself a favour and do the job right. The proper punchdown tool, rather than the plastic toy; keeping the twists in place; not pulling hard on the cable or putting excessively sharp bends in the route (a
1 inch/3cm min radius is good, 2in/5cm better); no nasty staples (they push the wires too close together), rather nice loose cable ties - that's the way to go. Do it right once, and forget about it for the next 10 years.HTH, Stefek