BUZZ-Go-Ahead: Investec upgrades, cites low exposure to GDP changes
** Public transport operator rises as much as 5.2 pct after Investec (LSE: INVP.L - news) raises rating on stock to 'buy' from 'add'
** Investec says only about 1/3 of co's business directly exposed to GDP changes
** Note (Stockholm: NOTE.ST - news) adds that Regional bus business most exposed; GTR unit does not have revenue risk
** Go-Ahead outperforms FTSE 350 Travel & Leisure Index which is -0.6 pct; stock 7% below pre-Brexit level