Ho un router belkin dove pero posso settare solo mtu ed arriva al max a 1492 non accetta valori piu grandi. Ho selezionato la scheda su drtcp e ho riavviato il pc. ecco i risultati di speed guide

CP options string = 0204055c0103030201010402
MTU = 1412
MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput.
MSS = 1372
MSS is not fully optimized for broadband (although it might work well for slower connections). Consider increasing your MTU value.
Default Receive Window (RWIN) = 256564
RWIN Scaling (RFC1323) = 2 bits (scale factor of 4)
Unscaled Receive Window = 64141

RWIN is a multiple of MSS
Other values for RWIN that might work well with your current MTU/MSS:
504896 (MSS x 46 * scale factor of 8)
252448 (MSS x 46 * scale factor of 4)
126224 (MSS x 46 * scale factor of 2)
63112 (MSS x 46)
bandwidth * delay product (Note this is not a speed test):

Your RcvWindow limits you to: 10262.56 kbps (1282.82 KBytes/s) @ 200ms
Your RcvWindow limits you to: 4105.024 kbps (513.128 KBytes/s) @ 500ms
MTU Discovery (RFC1191) = ON
Time to live left = 54 hops

TTL value is ok.
Timestamps (RFC1323) = OFF
Selective Acknowledgements (RFC2018) = ON
IP type of service field (RFC1349) = 00000000 (0)

grazie per l'aiuto!!