You've omitted mortgage amortisation from that calculation. £71 is the principal and interest payment so the 2046 mortgage balance should be zero. Correct figures to compare are £4.2k investments versus £3.98, so better off borrowing to invest.
This makes sense intuitively - obviously you make money if you borrow at 5% and invest at 6.16%. However, a 116 bps spread seems skinny to me when you consider risk and tax.
You've omitted mortgage amortisation from that calculation. £71 is the principal and interest payment so the 2046 mortgage balance should be zero. Correct figures to compare are £4.2k investments versus £3.98, so better off borrowing to invest.
This makes sense intuitively - obviously you make money if you borrow at 5% and invest at 6.16%. However, a 116 bps spread seems skinny to me when you consider risk and tax.