I run an IT support Company and we supply PC's to customer spec because as there IT company they want us to be a 1 stop shop.
IMO there is no money in it the hardware, the market has no decent margins - If you could beat PC world by 40% I'd buy all my PC's from you
We can't make 10% on a PC and be competitive, The profit is in quantity with PC's make £10 a box but sell 1000 boxes a week you have a business.
The big boys make as much out of the accessories as they do the PC - 2m USB cable PC world £3 -£9 I can buy them at £0.65. (ever noticed printers don't come with cables?)
Then as mentioned above - every time they have a problem you get a call.
I wish you all the best but (again IMO) the money in IT is in repair, software development or support roles. To make money on hardware it's all about quantity, accessories and "interest free" credit along with the warranties they sell you.
Good luck with whatever you decide though.