Your comment on using the BT speetester and ISP congestion makes sense to me.
Why don't you give AAISP a call and explain your situation. "I'm thinking of moving over but..." etc
They may have data on your exchange or even better existing customers on there.
I'd be tempted to move anyway to give it a go as their home::1 tariff with premium looks to be £8 a month cheaper than you are paying now.
The units tariff on 20cn may be OK for you depending on usage pattern and you could always use this for a month to give it a go and then change to Home::1 if all is good.
Prices are eye watering between 9am and 6pm but OK if you only use the net between 6pm and 9pm plus weekends.
6 month minimum term on Home::1 and restrictions on business use.